Lost Communication With Body Control Module
The engine control module lost communication with the body control module.
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What it means (plain English)
Inside your vehicle, the engine control unit (ECU) talks to various control modules like the body control module (BCM) to get information about systems like lights and locks. If this communication is interrupted or fails, you get a U0191 code.
What the computer is actually seeing
The ECU looks for a signal from the BCM and does not receive it within a specified time frame, often around 200-500 milliseconds.
What a healthy reading looks like
ECU should receive a consistent signal (voltage levels between 0.5V to 5V) from BCM during operation.
Guided diagnostic — the DiagCoach way
Don't just throw parts at it. Walk through these in order — each step tells you whether to keep going or stop and fix what you found.
- 11. Check for blown fuses related to the BCM in the fuse box. Replace any blown fuses and recheck the code.
- 22. Inspect the wiring and connectors between the ECU and BCM for damage, corrosion, or loose connections. Repair or replace as necessary.
- 33. Test the battery voltage; it should be between 12.4 to 12.8 volts with the vehicle off. Charge or replace the battery if voltage is low.
- 44. Use a scan tool to see if other communication codes are present; if there are multiple loss of communication codes, suspect a power or ground issue. If yes, troubleshoot that circuit first.
- 55. If needed, reprogram or replace the BCM if it is confirmed faulty through testing.
Common causes
- Faulty BCM
- Damaged wiring or connectors between ECU and BCM
- Bad ground connection for the BCM
- ECU software issue or corruption
- Battery voltage below 12V or unstable voltage supply
Typical repair cost
$$$
Related codes
Frequently asked questions
Is it safe to drive with this code?
Yes, but features controlled by the BCM may be disabled, so comfort and convenience are affected.
Will this code come back after clearing it?
It may return if the underlying issue isn't fixed, especially if there's a wiring issue or a faulty BCM.
Why does this code show up with other communication codes?
It's common for multiple communication issues to occur if there's a shared power or ground problem affecting multiple modules.
Working a real vehicle right now?
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